Nikola Tesla. Amazing guy. He came up with a huge number of inventions, but outside the scientific community he is largely overshadowed by his better known contemporary, Thomas Edison. Tesla developed a stream of innovations that we use every day—things like AC power, fluorescent lighting, on and on.

What you might not know is that Tesla, when working on electric light in February of 1894, came up with the concept for what we now call the Plasma Globe.

On a Bright Day:

A great deal of energy falls on the Earth’s surface – roughly 1 kW per square meter. This is about 0.6 Watt per square inch. This doesn’t sound like much energy, but suppose we collect and concentrate 63 square inches of this sunlight? These 63 square inches would collect about 38 Watts of energy. This doesn’t sound like much, but…

Suppose We Could Then:

Concentrate these 38 Watts into an area of only 1/8 of a square inch? This is exactly what we can do with an inexpensive plastic Fresnel lens. We’ll focus the sunlight into an area 3/8” in diameter – this is the equivalent of 300 Watts per square inch! With this energy level, we can easily ignite a piece of wood, boil some water, andeven melt a penny.

We’ve all likely encountered the time-consuming effort required to set up an optics demo; all the necessary components are on hand, but they don’t easily work together. The difficulty is obvious: the various components are either ‘loose’ or mounted at differing heights. Thus: wasted and frustrating time ‘shimming’ with books and pads to match the heights of the components.

The solution is simple: choose a height (above bench top) and mount every optical component at the same (optical centerline) height. But, how does one choose a height? Simple: first, determine the optical component with the highest centerline then second, build supports for all the other components – matching this centerline height.

I began with a 100 Watt clear light bulb mounted upon a wooden base – the center of the filament was 4-3/4” above the bench top. I then ensured that everything else I had, or planned to incorporate in demos, could be centered at this height.

The supports shown in the following illustrations are of ¾” pine – either screwed or glued together. Where required, various combinations of rubber feet and jackscrews provide support and positioning capability. When applicable, stacks of steel washers are incorporated to add stability. Read the rest of this entry »

Imagine students’ amazement when they actually see sunlight melt a penny with the Atomic Penny Vaporizer! This demonstration clearly illustrates the vast amount of energy illuminating the Earth’s surface. In rough numbers: 70% of the Sun’s incident energy on our outer atmosphere is reflected back into space – only about 30% actually gets to the Earth’s surface. But, as we experience, this is still a substantial quantity of energy.

Fortunately, this energy (I. R. – Visible – U. V.) is rather uniformly distributed over the Earth’s surface – thus its overall intensity is such that we have a habitable environment. However, as we all know, we can concentrate some ‘area’ of this energy to increase the ‘energy per area’ (a measure of this is the temperature of the area of concentrated energy). A common magnifying lens (2-4 in. diameter) will concentrate sufficient energy to burn paper or other objects with a low flash point. Read the rest of this entry »